US3044156A

US3044156A - Temperature resistant body

Info

Publication number: US3044156A
Application number: US438652A
Authority: US
Inventors: Marshall G Whitfield; Sheshunoff Victor
Original assignee: Individual
Current assignee: Individual
Priority date: 1954-06-23
Filing date: 1954-06-23
Publication date: 1962-07-17
Anticipated expiration: 1979-07-17

Description

July 17, 1962 M. G. WHITFIELD ETAL 3,044,156

TEMPERATURE RESISTANT BODY Filed June 25, 1954 EGJ.

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United States Patent O 3,4i,156 TEMPEEEATURE RESSTANT BDY lvlarshall G. Whiteld, 2 Harvard St., Garden City, NX., and Victor Sheshnnoii, P). Box '702, lviagnelia, Ark. Fiied .inne 23, 1954i, Ser. No. 438,652 7 Ciaiins. ttll. 29-194) The present invention relates to improved metal bodies constituted of tungsten or molybdenum and ferrous alloys thereof, and more particularly to metal bodies containing substantial percentages of tungsten and molybdenum protected against deterioration inV oxidizing atmospheres at high operating temperatures.

This is a continuation-in-part of our copending application, Serial No. 673,880, filed lune l, 1946, and entilted Oxidation Protected Tungsten and Molybdenum Bodies and Method of Producing Same, which has now matured into Patent 2,682,101, dated lune 29, 1954.

At the present time there are various industrial. developments where alloys of special character are necessary, capable of retaining their high mechanical strength at high operating temperatures. Examples of such applications are particularly parts for jet engines and gas turbines in which the demands made on the structural parts with respect to their strength at elevated operating temperatures are extremely exacting.

Materials now employed for these purposes generally comprise alloys of iron and of nickel, in many cases with additions of cobalt, chromium, tungsten and molybdenum. Even the alloys of tungsten and molybdenum, while theoretically promising, proved very disappointing in actual practice. ln general, few, if any, of these alloys had a useful life over 300 hours, necessitating frequent replacement of critically important structural elements at great trouble and expense.

As is known, tungsten and molybdenum are unstable when heated in air or in any other oxidizing atmosphere at temperatures in the range of 800 C., or above. The oxides formed on the surface of the tungsten and molybdenum bodies under such conditions sublime or boil away continuously V't0 such a pronounced degree that these metals can only be used in a pure reducing atmosphere of hydrogen, or of an inert lgas, such as argon, or in vacuum. The same difficulty is present with respect to alloys containing more than of tungsten and molybdenum. Of course, this circumstance greatly restricted or even negatived the usefulness or such metal bodies and, as a matter of fact, those skilled in the art strongly advised against the use of alloys containing tungsten and molybdenum in excess of 15% for high temperature applications. Although the outstanding problem was well known in the art and from time to time various suggestions and proposals were made to provide a solution therefor, none, as far as we are aware, of these suggestions and proposals was completely satisfactory and successful on a practical and industrial scale.

We have found that the problem may be solved in a remarkably simple and unique manner.

It is another object of the inventionV to provide a novel and improved method of preventing the surface sublimation and resulting deterioration of metal bodies constituted of tungsten, molybdenum, and alloys thereof when exposed Yto oxidizing atmospheres at elevated temperatures in the range of 800 C. and thereover.

It is a further object of the invention to provide a protective layer on the surface of tungsten and molybdenum bodies, said protective layer being essentially composed of an aluminum containing material.

It is also within the contemplation of the invention `to provide a novel method of protecting tungsten and molybdenum bodies against surface sublimation at high operating temperatures while exposed to oxidizing dlh Patented July l?, 1962 r ice j vmeans for avoiding the deterioration of protected bodies made `of or containing molybdenum or tungster or both due to excessive differences in coeicients of expansion as between the body and the coating.

Another object of the invention is the provision o coated bodies of the general class herein referred to in which beryllium is a constituent of the body or the coating or both.

Other and further objects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawing, in which:

FIG. l is a fragmentary sectional vview of a metal body embodying the principles of the invention during the process of its manufacture.

FIG. 2 is a similar View of an oxidation protected tungsten or molybdenum body having a bonding layer of nickel and a protective layer applied thereto, and

FIG. 3 is a longitudinal sectional view of a refractory metal body comprising a core of tungsten or molybdenum and having a partially `diffused protective layer thereon constituted of an alloy of protective elements and molybdenum or tungsten..

Y Broadly stated, according to the principles of the inf vention,the tungsten or molybdenum bodies to be protected are .coated preferably with a aluminum base-Inaterial which maybe pure aluminum or alloys rich in aluminum. This coating may be carried out by various procedures but best results are obtainedby a hot dip method in which the metal bodies to `be protected are immersed in a bath of molten metal for a predetermined length of time sufficient to provide a coating of the metal thereon. We have found that by this method there is formed a thin protective layer on the surface of the tungsten or molybdenum body which layer is essentially constituted of an alloy of coating metal with the base metal. Experimental work with tungsten and molybdenum bodies treated in accordance with the invention has indicated that these materials do not exhibit their normal oxide forming characteristics even at temperatures approximating the boiling point of aluminum and in many cases even at vtemperatures as high as 2000 C.

The bath of molten aluminum base material may be composed of high purity aluminum, commercially pure aluminum and of aluminum alloys having a relatively high aluminum content. Examples of such aluminum alloys are alloys containing 5% to 15% by weight of at least one of the elements selected from the group consisting ofiron, nickel, chromium, cobalt and beryllium, the balance being substantially all aluminum. In addition, various other aluminum base materials containing other and further constituents may be used..

'If desired, the bodies to be treated' with the bath of molten aluminum base material may be subjected to a preliminary cleaning by Sandblasting, burnishing and similar mechanical procedures. In most cases, however, such preliminary cleaning is not necessary. For example, rolled molybdenum sheet may be subjected to treatment by the bath of aluminium base material without any preliminary cleaning.

.The temperature of the bath of molten aluminum base material may be subject to considerable variations in Vinitial temperature of the bodies to be treated, on their thickness or mass and to some extent also on the operating temperature of the bath. The thickness of the coating of aluminum basematerial is not critical but may be in the order of 0.002." to 0.00.4".

ExaminationV of wire and sheet samples of .tungsten p and molybdenum, which have been treated with aluminum and exposed tohigh temperatures in oxidizing atmos-v -pheres, indcatestha't a high melting compound of aluminum .with the tungsten or molybdenumcorehas been` formed and that this alloy is free from the weness of either thev tungsten or molybdenum with regard to oxidizing tov form .a compound of low boiling or sublimation point on the surface. .For example, samples treated'iby the method of the invention have been heated Vto tempera- Atures a hundred degrees C. above the normal .boiling point Yof'aluminum before the aluminum boiled away, indicating that the alloysof aluminum with tungsten or molybdenum'have extremely high Vboiling or sublimationpoints. Likewise, it has been found'that the presence Vof aluminum on thesurfaceofthesemetals, will permit their use for .applications requiring substantial strength at `elevated temperatures. The method of the invention is applicable with equal or similar results also to alloys of at least one of the metals iron, nickel, cobalt with tungsten or molybdenum, or'both, containing substantial quantities of tungsten ormolybdenum, such as at leastl 15% by weight, Vand Valso to alloys of tungsten and molybdenum.

v Preferably, the aluminum coated tungsten and molybdenum containing bodies are ,heat treated'to assureV the formation lofa high melting compound of aluminum with the tungsten or molybdenum core and thereby .to obtain a completely stable product. Itis also possible, however, to omit-such' heat treatment andto rely on the diffusion of the aluminum coating into the refractory core during.V

'the actual operation at elevated temperatures. .If 'heat treatment is resorted to, the heat treating temperature may Abe in the order of 1300" C., although it is not restricted to 'such temperature.

in many cases copper and silver plates may provide equal 1 or similar results.

While theexact reason for the beneficial effect `of the v preliminary deposit of nickel or other iron group metal is not fully understood, it is believed that these metals form alloys with aluminum more quickly than do tungsten and molybdenum and that these electrodeposited films act as temporary protectors until the aluminum can form its alloy with the tungsten or molybdenum which have a tendency to oxidize even at relatively low temperatures, such as red heat."

Referring now to the drawing, in FIG. l there is shown a metal body embodying the principles of the invention which comprises a base or core 10 of tungsten or molyb denum. Upon both faces .of the core there is provided a thin coating 11 of aluminum or aluminum base material constituting a protective layer for the core. Of course, in actual manufacture, layer 11 is initially a coating of aluminum containing sometungsten or molybdenum and is bonded to the core by an aluminum rich alloy of these refractory metals caused by partial diffusion of the aluminum into the core. In service, or in the final stage of manufacture, the excess `aluminum is partly oxidized and partly diffused to produce the alloy surface layer which is referred to in the foregoing. K

FIG. 2 illustrates an example of the modification of the 'invention in which the tungsten or molybdenum core 20 is first coated with a thin iilm of nickel or other iron base metal 2l and thereafter is exposed to the eect of a molten bath of aluminum base material, such as, for example, commercially pure aluminum, thereby forming a protective layerZZ onV the exterior Aof the core. As arresult of the interaction of the core material With that of the layers `21 and 22 during the heating and coating'treatments and .'"While the methodoffthe invention providesV excellent v. results in protecting and stabilizing tungsten and molyb-` denum bodies, when .treating these metals with `aluminum or its alloys, occasionally small spots or areas are found which are ralloyed only with extreme ditiiculty. VWe .have found that 4this diiculty may be completely avoided by electrodepositing a thin film Vorrlayer of nickelron the V,surface of ther tungsten or molybdenum and diffusing or Y at leastheating the nickel plated sections in a non-oxidizing or reducing atmosphere at approximately .l000 C.y

with aluminum. This modification of the methodl of the 'before treating the sections of tungsten or molybdenum Y The thickness of the electrodeposited nickel layer is v not criticaland maybeasubjected to considerable Vvariations. In this connection, it may be observed that dijlul sion of the nickel layer maybe accomplished not only by layer is accomplished by the heating eiect of the bath of aluminum base material, and the bath at the same time provides the non-oxidizing or protective environment.

It has been found that nickel is not the only metal which subsequent service operation, the metal body is converted into the one shown in FIG; 3 wherein the individual existence` of layers Zyl and 22-has practically disappeared, such layers being combined intoa layer 23` which is composed of an alloy rich in aluminum and-containing appreciableamounts of nickel and tungsten or molybdenum.

While in the drawing fragmentary sectional views of 1 refractory metal strips are shown which are coated with a layer of aluminum base material on both facesthereof, in actual practice, the refractory metal bodies are provvidedwith a protective layer of the described character throughout their entire surface, including their ends and edges. In this manner, the said metal bodies are fully protected from Ydeterioration at elevated operating tem- '.peratures.

In order to facilitate understanding of the invention by those skilled in Athe art, the following illustrative examples may be given:

' having a temperature of 720 C., for 6 minutes. After removal from the bath and cooling, the materialwas tested by heating it to 1400-1500 C. in an oxidizing atmosphere for 4 hours, without noting `any appreciable deterioration.

' Example II A. molybdenum sheet about 0.020" thick was cleaned and a light coating of nickel was electrodeposited thereon. The plated sheet was heated for a few minutes in a reducing atmosphere at approximately 1000" C. The sheet was .cooled and then treated by immersing in a bath of molten commercially pure aluminum, having a temperature of 740 C., for 3 minutes.

Although the present invention has been described in with each other or with other metals. The advantages of the invention in the case of tungsten and molybdenum alloys are particularly accentuated when such alloys contain at least by weight of tungsten or molybdenum, or tungsten and molybdenum combined.

The teachings hereinabove made and the `examples hereinabove given, applying to the coating of tungsten or molybdenum bodies (as defined) with aluminum or aluminum alloys (as dened), apply as well to the use of the metals silicon and beryllium as constituents of the initial coating. One of the purposes of the present invention is to avoid extraordinary discrepancies between the coefficients of expansion of the base metal and the coating material. As compared with aluminum which has a high coefficient of expansion, tungsten and molybdenum bodies have relatively low coeihcients of expansion.

it has hitherto been known that the alloying of relatively large quantities of silicon with aluminum will provide a metal composite having a relatively lower coeicient of expansion, and in particular a coefficient of expansion substantially closer to that of ferrous bodies. For such purposes, as much as from 25% to 30% or more of silicon hasbeen alloyed with aluminum.

It has been found, however, that such very large quantities of silicon give an aluminum alloy material which is more difficult to use in molten `form as a hot dipping medium, and also that the formation of an adequate bond between the alloy layer and ferrous base metals is rendered more dicult.

Beryllium is a metal which has a coetiicient of expansion substantially less than half that of aluminum. We have found that beryllium may be alloyed withaluminum to provide alloys having coetlcients of expansion much closer to that of ferrous bodies and tungsten and molyb\ denum bodies as herein dened. When beryllium is added to aluminum, it is readily possible to secure coating alloys having coeiiicients of expansion very much lower than that of aluminum alone, and in particular coefficients of expansion substantially corresponding with those of conventional ferrous bodies, with the beryllium within the ranges set forth above, namely from about 5% to about 15%, and up to about 50% of the alloy.

It is readily possible to employ beryllium along with silicon., For example, an alloy can be formed of aluminum containing about 5% to 15% of beryllium and 5% to 50% silicon, balance being aluminum.

Beryllium in substantial quantities thus is seen to be a valuable component of aluminum or aluminum alloys used for coating where the object is to attain in the coating a coeicient of expansion much more nearly corresponding to that of the base metal, whether the base metal is to be coated by hot dipping or by the casting of the alumi-` num alloy against it. Moreover, beryllium has a substantially lessened tendency to interfere with the formation of a strong bond between the aluminum alloy and the base metal upon which it is coated.

In the formation of tungsten or molybdenum bodies which are to withstand oxidative deterioration at the high temperatures mentioned herein, the beryllium does not interfere with the action hereinabove described. In fact, tungsten and molybdenum bodies, resistant to oxidative deterioration at high temperatures, can be produced by coating tungsten or molybdenum bodies (as deiined) with beryllium alone, in spite of the high avidity of the last named metal for oxygen. The use of interface A metal coatings as hereinabove disclosed between the aluminum alloy' and the base 'metal is equally veffective with beryllium alone or with valuminum alloys containing beryllium or beryllium and silicon.

In the production of coated bodies having a minimum difference between the coefficients of expansion of the bodies `and the coatings thereon, it is possible not only to diminish the coeicient of expansion of the coatings, but also to raise the coetiicient of expansion of the bodies. Where tungsten and molybdenum bodies are spoken of above, not only are bodies of pure molybdenum or tungsten or mixtures of the two contemplated, but also ternary or complex alloys containing at least substantially 15% of tungsten or molybdenum or a mixture of the two. The coefficient of expansion of such ternary or complex alloys is higher than that of molybdenum or tungsten alone. But it is possible to raise the coetlcient of expansion of such bodies by alloying the molybdenum or tungsten or ternary alloys containing them with such elements as chromium. This may ordinarily be done without sacrice of desirable physical properties.

When coating tungsten or molybdenum or ferrous bodies with beryllium or aluminum alloys containing beryllium, a protective `atmosphere will normally be maintained over the bath'since beryllium is more subject to oxidation than aluminum.

Modications may be made in the invention without departing from the spirit of it. The invention having been described in certain exemplary embodiments, what is claimed as new and desired to be protected by Letters Patent is:

l. A body formed from metal chosen from a class consisting of tungsten, molybdenum, mixtures of the two, Kand ferrous alloys containing at least 15 of any of the foregoing, bot coated with a bonded layer of aluminum containing substantially 5% to 50% beryllium.

2. A body formed from metal chosen from a class consisting of tungsten, molybdenum, mixtures of the two,

'an-d ferrous alloys containing at least 15% of anyy of the foregoing, hot coated with a bonded layer of'aluminum containing substantially 5% lto 15% beryllium, and substantially 5% to 15% silicon.

3. As a new article of manufacture, a refractory metal tbody protected from surface deterioration Iat lelevated operating temperatures comprising la core constituted of a refractory metal selected from the group consisting of tungsten, molybdenum, alloys of tungsten and molybdenum, and alloys containing at least 15% of any of the foregoing with at least yone of the metals iron, nickel, cobalt and chromium, and `a protective layer on said core of aluminum containing substantially 5% to 15% beryllium.

4. As a new `article of manufacture, a refractory metal body protected from surface deterioration at elevated operating temperatures comprising -a core constituted of a refractory metal selected from the group consisting of tungsten, molybdenum, alloys of tungsten and molybdenum, and `alloys containing at least 15% of any of the foregoing with at least one of the metals iron, nickel, cobalt and chromium, Iand `a protective layer on said core of aluminum containing substantially 5% to 15 beryllium, and substantially 5% to 50% silicon.

5. The structure claimed in claim 3, with a thin inter- (References on following page) 'Y ff Referenes' cited in the fue df this patent Y VUNITEDswmgs VPATENTS,

`Mml: Sept. n 28, 1915 Archer ..l June 11, 1929- Weiger May 31,1932 VHorselcl Sept. 27, 1932 Nook Dec. 1, 1936 Schwarzkopf Oct. 26,l 1937 Kruh June 21, 1938V S Y Whie1d' Nov. 8, 1938 Sittings Aug. 28, 1951 v Shepard ,Mar. 11, 1952 Campbell Ian. 12, 1954 Whiteld June 29, 1954 FOREIGN PATENTS Great Britain July 8, 1926 Frame Apr. 8, 1932

Claims

1. A BODY FORMED FROM METAL CHOSEN FROM A CLASS CONSISTING OF TUNGSTEN, MOLYBEDEUM, MIXTURE OF THE TWO AND FERROUS ALLOYS CONTAINING A LEAST 15% OF ANY OF THE FOREGOING, HOT COATED WITH A BONDED LAYER OF ALUMINUM CONTAINING SUBSTANTIALLY 5% TO 50% BERYLIUM.